1. Field of Invention
The present invention relates to a disk for a disk drive, and more particularly, to a disk, at least one surface of which is provided with a signal recording portion to record and reproduce signals in a disk drive.
2. Description of the Prior Art
Disks (for example, CDs or DVDs) are used as media for recording and reproducing digital data. The recording and reproduction of the digital data in the disk is performed in a disk drive. FIG. 1 shows a plan view of the disk according to a prior art.
As shown in the figure, a disk 10 comprises a disk body 12 shaped in a circular disk. The center of the circular disk body 12 is formed with a center through hole 14. The center through hole 14 with a predetermined diameter is bored through the center of the disk body 12.
The center through hole 14 is fitted onto an insertion cone provided on a turntable of the disk drive. That is, an inner peripheral surface of the center through hole 14 is fitted onto an outer peripheral surface of the insertion cone.
A clamping portion 16 with a predetermined width is formed around the center through hole 14. A lower surface of the clamping portion 16 is seated onto the turntable. A clamp for fixing the disk 10 to the turntable is seated onto an upper surface of the clamping portion 16. In a case where in the disk drive, the insertion cone is provided with the clamp, the upper surface of the clamping portion 16 is not naturally used for the disk to be clamped.
A signal recording portion 18 ranges from an outside of the clamping portion 16 to a rim of the disk body 12. The signal recording portion 18 is provided with a signal recording section 19, inner and outer rims of which are formed with inner and outer rim sections 20 and 20′, respectively. The inner rim section 20 is a boundary between the clamping portion 16 and the signal recording section 19.
However, the above prior art has the following problems.
That is, as shown in FIG. 2, in the conventional disk 10, cracks c occur on an outer rim of the center through hole 14. This is the reason why a force may be applied thereto while a friction is generated between the outer rim of the center through hole 14 and the insertion cone in a process of seating and separating the disk 10 onto and from the turntable. Particularly, in a case where the insertion cone has the structure for clamping the disk 10, the cracks c easily occur.
In addition, as the speed of the disk drive has been recently increased at a high multiple access speed, the rotation rate of the disk 10 generally increases to 8,000 rpm or more. However, if the rotation rate of the disk 10 increases, causing a centrifugal force to increase, the cracks occurring on the outer rim of the center through hole 14 gradually propagate up to the signal recording portion 18. In a severe case, it may be possible not to use the disk since the disk body 12 is completely broken. Furthermore, some broken pieces of the broken disk body 12 spatter outward, so that users may be injured.